The present invention relates to cartridge strip magazines for holding propellant cartridges to be fed to repeating, powder-actuated fastener setting tools.
A cartridge magazine of one of the more widely used types conventional prior to the present invention is seen in U.S. Pat. No. 3,611,870, which describes a strip with conical projections with a cone angle greater than that of the chamber in which they are to be used. The present invention provides an alternative to and improved replacement for the prior art cartridge magazine band of U.S. Pat. No. 3,611,870.
Most explosion driven bolt setting tools customarily have a forwardly biased barrel axially slidable within a housing, the tool being operable for safety reasons only when the barrel muzzle is pushed against the target so as to push the barrel breech to the rear adjacent a firing pin. In such tools, the barrel breech customarily has a substantially coaxially arranged cartridge chamber which moves with the barrel in an axial direction as the barrel slides. Many of such tools have since the early 1960's had a conical cartridge chamber and since the mid 1960's have had a magazine feed channel extending substantially perpendicularly to the main axis of the tool for receiving a cartridge magazine and allowing the magazine to feed across the main axis of the tool. Tools with conical cartridge chambers are predominate at the present time and it is for use in such tools that the present invention is intended. The cartridges in such a tool must be arranged substantially parallel to the main axis of the tool once the cartridge magazine is put into the magazine feed channel. When the barrel is moved rearward the respective cartridge which extends coaxially to the cartridge chamber must be introduced into the cartridge chamber. The cartridge magazine used for such an application must be a relatively flat strip of plastic material which also projects from the strip so as to surround the lower walls of the cartridge and seal against a conical chamber. Cartridge magazine strips of the general type in which the cartridge remains held within the magazine strip before, during and after firing have been known since at least the first World War. Since about 1960 it has been customary to surround the cartridges with frustoconical plastic shrouds having a cone angle equal to or greater than that of a corresponding conical cartridge chamber. The obvious application of such magazines to repeating setting tools was made in the mid-to-late 1960's. Since conical plastic shrouded rounds and conical cartridge chambers were in wide use it was simplest that plastic conical shrouds be part of such strips. The adoption of such conical plastic shrouds (single or in strip) was further suggested by the fact that cartridges in resilient conical plastic shrouds were well known as a means of making the cartridge self-eject due to their resilience without need for mechanical ejectors in the tool, and eliminates the need to shake spent cartridges out of the chamber. Stripping of ammunition has been conventional since the advent of the machine gun and multiple fire setting tools have been known since the late 1950's. However, prior art conically shrouded multiple round magazines are known to have a tendency of misfire (fair to fire) or leak gas. A solution to these problems is needed.
The cartridge must fit tightly in the cartridge magazine so that the cartridge will not remain in the cartridge chamber when the tool is removed from the target and the barrel moves forward but rather will remain with the magazine and thus be removed from the cartridge chamber of the barrel.
This invention provides a new and useful cartridge magazine strip having non-conical stepped projections which define cartridge receiving recesses at fixed spaced locations along the length of the strip and which have an internal dimension small enough to cause the projections to pressure engage the exterior of a cartridge and to surround the cartridge adjacent the base thereof but to allow the top end of the cartridge to project outwardly therefrom, the cartridge holding projections having a stepped exterior surface which both facilitates a quick release from a conical inner wall surface of the cartridge chamber defined by the barrel of a fastener setting tool and provides multiple sealing points and a shock absorbtion cavity between the projections and barrel chamber.
In accordance with the invention there is provided a strip magazine designed as a disposable magazine for receiving and surrounding the walls of a cartridge. The magazine includes stepped projections on the front side of the strip. The base of the cartridge fits into the recess of the strip and its bottom end is preferably aligned flush with the back side of the strip. The cartridges are held in the recesses with a press-fit. The outside walls of the strip projections are stepped in decreasing external diameter toward the tip of the associated cartridge from the cartridge bottom. By making the projections which define the cartridge receiving recesses with the non-conical stepped configuration it is possible to use the magazine in connection with a setting gun having a barrel chamber which is conically formed yet still provide even aligned feeding of the cartridge into the conical barrel cartridge chamber. In addition, the steps of the projections abruptly reduce the outside diameter of the projections to both (a) give multiple high pressure sealing points with a shock absorbing cavity therebetween and (b) reduce the contact surface area between chamber wall and projection to help prevent self-locking of the cartridge or of the cartridge magazine itself within the conical cartridge chamber of the gun barrel. In this way jamming of the cartridge or strip in the cartridge chamber of the gun barrel is avoided yet it is ensured that the cartridge will both be sealed in the chamber during firing and remain in the magazine and be withdrawn from the gun after firing due to the feeding movement of the magazine.
Since power tool cartridges are conventionally rimmed, to achieve a tight fit of the cartridge in the cartridge magazine recesses it was previously felt sufficient if the cartridges are held by the magazine only in an area adjacent the rim. However, in order to positively avoid splitting ("bursting") of rimfire cartridge cases, particularly with conical cartridge chambers, it is necessary that the cartridge strip is formed to embrace the cartridge approximately up to the cartridge crimp region in which the tubular projection forming the cartridge recess is of a minimum wall thickness so that the gap from the unsupported projecting portion of the cartridge case to the wall of the cartridge chamber defined by the gun barrel will be a minimum. In the preferred embodiment of the invention the cartridge magazine embraces the cartridge for slightly more than 2/3 of its height, i.e., up the cartridge wall to the bottom of the crimped forward end of the cartridge. The magazine also engages the rimmed bottom or base of the cartridge around its periphery or rim. The magazine is constructed so that the parts thereof which are exposed to high pressures and temperatures during the explosion and the burning powder gases will not melt or flow and lose their sealing ability in the chamber because gas flow in a direction opposite to the driving direction along with any backward blow off of the propellant gases must be prevented or the strip will be burnt apart ("shot off") between the projections. The construction is such that the stepped cartridge magazine projections are supported by the conical chamber when the tool barrel is in the firing position, the support being both at the location of the stepped projections and the strip between adjacent projections.
The cone angle of any conically tapered parts of the stepped cartridge magazine projections is made slightly less (skinnier cone) than the cone angles of the conical cartridge chamber of the barrel of the receiving gun so that the forward or outer edge of the step forms a sealing ring. Alternately, if the projection is of a non-conical arcuate shaped exterior, the sealing point would be toward the middle of the arc, specifically at the point where a tangent to the arc would be parallel to the conical inner surface of the chamber. The cartridge chamber wall and these sealing rings of the cartridge magazine must come in contact with each other preferably both adjacent the part of the cartridge chamber which faces the cartridge magazine and at or near the projection tip so that an increased compressive stress on the plastic is ensured in these contact region when the gun is pressed against the target material and to provide a shock absorption cavity between the sealing rings. These sealing rings prevent the cartridge contained in the cartridge chamber from shifting forward axially and the necessary ignition energy can thus be kept very low. Under the action of the firing pin the smaller cone angle (i.e., steepness) of the walls of the steps relative to the chamber walls causes the leading edge to serve as the sealing point rather than the rear of the projection as was previously thought necessary. Using the leading edge as the sealing point gives the seal greater strength since the step, which is highly compressed by the chamber walls in the firing position, is most difficult to further compress to allow firing gas to pass; whereas if the trailing edge is the sealing point bending might let gas to pass. Also, the steepness of each of the steps is a cone angle less than the cone angle chamber and this makes the steps stronger since the steepness results in the forces on the step being directed more along the axis of the projection than would be the case if the steps were less steep. Furthermore, the shock absorption cavity will be at a higher gas pressure than the gas pressure in the portion of the chamber forward of the projection due to the combined effect of the barrel precompressing the projection (and hence the cavity) and the compresion of the cavity due to case expansion. This cavity pressure also encourages self-ejection of the strip from the chamber.
Accordingly, it is an object of the invention to provide an improved magazine construction which includes a base member such as a belt or band having a plurality of steeply stepped tubular projections forming cartridge receiving recesses of a dimension such that the magazine will embrace each cartridge adjacent its lower portion and hold it with a press-fit, the outer wall of the tubular projections being steeply stepped for improved sealing and easy release from a conical cartridge chamber of a gun barrel. The steps may alternatively be arcuate.
A further object of the invention is to provide a cartridge magazine which is simple in design, rugged in construction, and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.